On the basis of analysing the outer performance degradation of shock absorber on suspenson and from the relationship between outer and inner performances of the shock absorber, an internal relationship between the str...On the basis of analysing the outer performance degradation of shock absorber on suspenson and from the relationship between outer and inner performances of the shock absorber, an internal relationship between the structure design and degradation of the shock absorber is discussed in the paper. From dynamic property, analysed the dynamic cause for degradation, the paper proposes a technical method of improving outer performance and a concept of critical velocity, and discusses what effects the critical velocity and the outer performance mance degradation has.展开更多
Sediments are ultimate sinks of nutrients in lakes that record the pollution history evolutionary processes, and anthropogenic activities of a lake. However, sediments are considered as inner sources of environmental ...Sediments are ultimate sinks of nutrients in lakes that record the pollution history evolutionary processes, and anthropogenic activities of a lake. However, sediments are considered as inner sources of environmental factor changes such as the variation in hydrodynamic conditions because of the nutrients they release. How does this process happen？ This study investigates a typical nutrient phosphorus （P） exchange among sediment, suspended particle matter （SPM）, and water. Compared with numerical and experimental studies, this study confirms that the critical velocity that occurs at a lower flow rate state exists in the range of 7 to 15 crn/sec. Critical velocity below the critical flow rate promotes the migration of particulate phosphorus （PP） to the SPM. On the other hand, critical velocity above the critical flow rate promotes the release of PP in water.展开更多
The dynamics of the moving-with-constant-velocity internal pressure acting on the inner surface of the hollow circular cylinder surrounded by an infinite elastic medium is studied within the scope of the piecewise hom...The dynamics of the moving-with-constant-velocity internal pressure acting on the inner surface of the hollow circular cylinder surrounded by an infinite elastic medium is studied within the scope of the piecewise homogeneous body model by employing the exact field equations of the linear theory of elastodynamics.It is assumed that the internal pressure is point-located with respect to the cylinder axis and is axisymmetric in the circumferential direction.Moreover,it is assumed that shear-spring type imperfect contact conditions on the interface between the cylinder and surrounding elastic medium are satisfied.The focus is on the influence of the mentioned imperfectness on the critical velocity of the moving load and this is the main contribution and difference of the present paper the related other ones.The other difference of the present work from the related other ones is the study of the response of the interface stresses to the load moving velocity,distribution of these stresses with respect to the axial coordinates and to the time.At the same time,the present work contains detail analyses of the influence of problem parameters such as the ratio of modulus of elasticity,the ratio of the cylinder thickness to the cylinder radius,and the shear-spring type parameter which characterizes the degree of the contact imperfection on the values of the critical velocity and stress distribution.Corresponding numerical results are presented and discussed.In particular,it is established that the values of the critical velocity of the moving pressure decrease with the external radius of the cylinder under constant thickness of that.展开更多
In most practical engineering applications,the translating belt wraps around two fixed wheels.The boundary conditions of the dynamic model are typically specified as simply supported or fixed boundaries.In this paper,...In most practical engineering applications,the translating belt wraps around two fixed wheels.The boundary conditions of the dynamic model are typically specified as simply supported or fixed boundaries.In this paper,non-homogeneous boundaries are introduced by the support wheels.Utilizing the translating belt as the mechanical prototype,the vibration characteristics of translating Timoshenko beam models with nonhomogeneous boundaries are investigated for the first time.The governing equations of Timoshenko beam are deduced by employing the generalized Hamilton's principle.The effects of parameters such as the radius of wheel and the length of belt on vibration characteristics including the equilibrium deformations,critical velocities,natural frequencies,and modes,are numerically calculated and analyzed.The numerical results indicate that the beam experiences deformation characterized by varying curvatures near the wheels.The radii of the wheels play a pivotal role in determining the change in trend of the relative difference between two beam models.Comparing the results unearths that the relative difference in equilibrium deformations between the two beam models is more pronounced with smaller-sized wheels.When the two wheels are of equal size,the critical velocities of both beam models reach their respective minima.In addition,the relative difference in natural frequencies between the two beam models exhibits nonlinear variation and can easily exceed 50%.Furthermore,as the axial velocities increase,the impact of non-homogeneous boundaries on modal shape of translating beam becomes more significant.Although dealing with non-homogeneous boundaries is challenging,beam models with non-homogeneous boundaries are more sensitive to parameters,and the differences between the two types of beams undergo some interesting variations under the influence of non-homogeneous boundaries.展开更多
Critical velocity of an infinite long sandwich shell under moving internal pressure is studied using the sandwich shell theory and elastodynamics theory. Propagation of axisymmetric free harmonic waves in the sandwich...Critical velocity of an infinite long sandwich shell under moving internal pressure is studied using the sandwich shell theory and elastodynamics theory. Propagation of axisymmetric free harmonic waves in the sandwich shell is studied using the sandwich shell theory by considering compressibility and transverse shear deformation of the core, and transverse shear deformation of face sheets. Based on the elastodynamics theory, displacement components expanded by Legendre polynomials, and position-dependent elastic constants and densities are introduced into the equations of motion. Critical velocity is the minimum phase velocity on the desperation relation curve obtained by using the two methods. Numerical examples and the finite element （FE） simulations are presented. The results show that the two critical velocities agree well with each other, and two desperation relation curves agree well with each other when the wave number k is relatively small. However, two limit phase velocities approach to the shear wave velocities of the face sheet and the core respectively when k limits to infinite. The two methods are efficient in the investigation of wave propagation in a sandwich cylindrical shell when k is relatively small. The critical velocity predicted in the FE simulations agrees with theoretical prediction.展开更多
The particle acceleration behavior and deposition mechanism of cold spraying aluminum matrix composites(Al_(2)O_(3)/2024)are complicated by the addition of ceramic particles.The effects of different feeding rates and ...The particle acceleration behavior and deposition mechanism of cold spraying aluminum matrix composites(Al_(2)O_(3)/2024)are complicated by the addition of ceramic particles.The effects of different feeding rates and particle diameters on critical velocity and mechanical properties were studied by numerical simulation and experiment.The results indicate that as the powder feeding rate increases,the impact velocity of gas and particles gradually decreases,and the temperature of gas and particles increases,resulting in an increase in the difference between particle impact velocity and critical velocity.The highest tensile strength of the deposit is achieved at a powder feeding rate of 1 r/min,which is 343 MPa.As the powder feeding rate increases,the performance of the deposits decreases,but it significantly saves time and cost.As the particle diameter increases,the impact temperature first increases and then decreases,resulting in the critical velocity first decreasing and then increasing,and the mechanical performance first increasing and then decreasing.To some extent,the best performance of the deposit is achieved when the size of the metal particle is close to that of the ceramic particle.展开更多
Presents the calculation of critical velocity, natural frequency and dynamic respondency of fluid conveying pipe are calculated under different boundary conditions using finite element method, and the use of calculati...Presents the calculation of critical velocity, natural frequency and dynamic respondency of fluid conveying pipe are calculated under different boundary conditions using finite element method, and the use of calculation results to design and research rocket pipes feeding fuel and watery turbine pipes conveying water etc.展开更多
In actual line operation,the critical velocity is one of the key physical quantities of rail design owing to its great infuence on the riding comfort and safety of vehicles due to the wheel-rail contact loss caused by...In actual line operation,the critical velocity is one of the key physical quantities of rail design owing to its great infuence on the riding comfort and safety of vehicles due to the wheel-rail contact loss caused by the abrupt change of rail foundation rigidity,rail wear,or abruptness irregularities on rail.In this study,the short floating slab track(SFST)structure is regarded as a double-layer system.The Euler beam and the rigid body model are adopted for the rail and the floating slab,respectively.and the dispersion equation and the theoretical critical velocity of the rail structure under ideal conditions are deduced.Besides,this st udy considers the implementation of the SFST in the vehicle-structure coupling system.The alterable element method is introduced for accurately simulating the change of the whee-rail contact state and coding a vehicle-structure dynamic analysis program(VSDAP)to calculate the critical velocity of rail structures from the dynamic response of vehicles and rail structures.The principle of its design at the beginning of the design is given on the basis of the theoretical value of the critical velocity and the simulation of the dynamic response,which can provide reference for practical engineering design.展开更多
Accurately predicting the minimum velocity required to initiate particles movement on a cuttings bed surface during drilling operations is crucial for efficient and cost-effective removal of deposited particles.Howeve...Accurately predicting the minimum velocity required to initiate particles movement on a cuttings bed surface during drilling operations is crucial for efficient and cost-effective removal of deposited particles.However,current models neglect the influence of particle shape on the drag coefficient and static friction coefficient during rolling and sliding on a cuttings bed.Accordingly,this study developed an experimental setup for cuttings transport and employed both theoretical analysis and experimental methods to investigate the critical velocity for the incipient motion of particles under various operational conditions.A novel semi-mechanical criterion model was developed for the incipient motion of particles,incorporating a shape correction factor for non-spherical particles.A balance equation for the threshold Shields number,determined by particle driving forces and resistances,was established,and a numerical procedure was formulated to determine the critical velocity for the incipient motion of particles.The model predictions show strong agreement with experimental results.The study found that higher eccentricity,inclination,and fluid viscosity increased the difficulty of initiating particle movement on the cuttings bed surface,thus requiring higher annular velocities for effective cuttings removal.Conversely,increasing particle size facilitated easier removal of the cuttings bed.Compared to non-Newtonian fluids,Newtonian fluids proved more effective in cuttings removal.The findings of this study are significant for optimizing hole cleaning parameters and improving the efficiency of cuttings removal.展开更多
The objective of this study is to investigate critical velocity and smoke maximum temperature beneath the ceiling in the connected area of branch tunnel with varying fire locations.The fire sources were located in the...The objective of this study is to investigate critical velocity and smoke maximum temperature beneath the ceiling in the connected area of branch tunnel with varying fire locations.The fire sources were located in the divergent connected area of the branch tunnel,to imitate traffic accidents near the branch point.A 1/20 scale model branch tunnel was built including main line before branch,main line after branch,and ramp.Experimental tests and numerical simulations were performed to explore smoke movement characteristics with longitudinal ventilation.The results showed that the enlarged cross-sectional area in branch tunnel caused the shortening of the back-layering length,and a modified model of back-layering length was proposed.The higher tunnel height in this work affected the critical condition of large fire;it caused a larger transition point of dimensionless critical velocity.A revised model was proposed for the maximum temperature rise of tunnel fires in the connected area of branch tunnel.The critical velocity kept unchanged when the branch angle increased from 0°to 20°because there is little change in the longitudinal smoke temperature.As the local tunnel width of fire source was increased,the required critical velocity was increased while the local effective velocity kept nearly the same.展开更多
Hydraulic collecting and pipe transportation are regarded as an efficient way for exploiting submarine mineral resources such as the manganese nodules and ores.Coarse particles on the surface of the sea bed are sucked...Hydraulic collecting and pipe transportation are regarded as an efficient way for exploiting submarine mineral resources such as the manganese nodules and ores.Coarse particles on the surface of the sea bed are sucked by a pipe during the mining and crushing of the mineral.In this paper,the critical suction velocity for lifting the coarse particles is investigated through a series of laboratory experiments,and the solid-liquid two-phase flow characteristics are obtained.Based on the dimensional analysis,the geometric similarity is found between actual exploitation process and model test with the same kind of material.The controlling dimensionless parameters such as the hydraulic collecting number,the relative coarse particle diameter,the relative suction height,and the density ratio are deduced and discussed.The results show that the logarithm in base 10 of the hydraulic collecting number increases approximately linearly with the increase of the relative suction height,while decreases with the relative particle diameter.A fitting formula for predicting the critical suction velocity is presented according to the experimental results.展开更多
The purpose of this paper is to study the critical sand starting velocity and transformation law of flow pattern based on gas-water-sand three-phase flow in an inclined pipe.Firstly,the indoor simulation experiment sy...The purpose of this paper is to study the critical sand starting velocity and transformation law of flow pattern based on gas-water-sand three-phase flow in an inclined pipe.Firstly,the indoor simulation experiment system of gas-water-sand three-phase flow was used to test the conversion law of flow pattern based upon the different gas void fraction.Secondly,the influence of slug bubbles on sand migration was investigated according to distinctive hole deviation angles,gas void fraction and sand concentration.Finally,the critical sand starting velocity was tested based on dissimilar hole deviation angles,gas void fraction,sand concentration and sand particle size,and then the influence of the abovementioned key parameters on the sand starting velocity was debated based on the force analysis of the sand particles.The experimental results illustrated that when the gas void fraction was less than 5%,it was bubbly flow.When it increased from 5%to 30%,the bubbly flow and slug flow coexisted.When it was between 30%and 50%,the slug flow and agitated flow coexisted.When it reached 50%,it was agitated flow.Providing that the hole deviation angle was 90°,the phenomenon of overall migration and wavelike migration on the surface of sand bed was observed.On the contrary,the phenomenon of rolling and jumping migration was recognized.The critical sand starting velocity was positively correlated with the hole deviation angle and sand particle size,but negatively associated with the gas void fraction and sand concentration.This research can provide a certain reference for sand-starting production in the field of petroleum engineering.展开更多
Full-scale numerical experiments were carried out on the vehicular fire in a long tunnel to study the critical ventilation velocity and back-layer distance with heat release rate of 5, 20 and 100 MW respectively. A co...Full-scale numerical experiments were carried out on the vehicular fire in a long tunnel to study the critical ventilation velocity and back-layer distance with heat release rate of 5, 20 and 100 MW respectively. A computational fluid dynamics (CFD) model of fire-driven fluid flow FDS(Fire Dynamics Simulator) was used to solve numerically a form of the Navier-Stokes equations for fire. The results were compared with the expressions proposed in the literature. A modified equation for the critical ventilation velocity was given to better fit the experimental results. A bi-exponential model that well fitted the numerical experimental results was proposed to describe the relationship between back-layer distance and ventilation velocity.展开更多
The current research of direct yaw moment control（DYC） system focus on the design of target yaw moment and the distribution of wheel brake force. The differential braking intervention can effectively improve the lat...The current research of direct yaw moment control（DYC） system focus on the design of target yaw moment and the distribution of wheel brake force. The differential braking intervention can effectively improve the lateral stability of the vehicle, however, the effect of DYC can be improved a step further by applying the control of vehicle longitudinal velocity. In this paper, the relationship between the vehicle longitudinal velocity and lateral stability is studied, and the simulation results show that a decrease of 5 km/h of longitudinal velocity at a particular situation can bring 100° increasing of stable steering upper limit. A critical stable velocity considering the effect of steering and yaw rate measurement is defined to evaluate the risk of losing steer-ability or stability. A novel velocity pre-control method is proposed by using a hierarchical pre-control logic and is integrated with the traditional DYC system. The control algorithm is verified through a hardware in-the-loop simulation system. Double lane change（DLC） test results on both high friction coefficient（μ） and low μ roads show that by using the pre-control method, the steering effort in DLC test can be reduced by 38% and 51% and the peak value of brake pressure control can be reduced by 20% and 12% respectively on high μ and low μ roads, the lateral stability is also improved. This research proposes a novel DYC system with lighter control effort and better control effect.展开更多
The aerodynamic unstable critical wind velocity for three-dimensional open cable-membrane structures is investigated. The geometric nonlinearity is introduced into the dynamic equilibrium equations of structures. The ...The aerodynamic unstable critical wind velocity for three-dimensional open cable-membrane structures is investigated. The geometric nonlinearity is introduced into the dynamic equilibrium equations of structures. The disturbances on the structural surface caused by the air flow are simulated by a vortex layer with infinite thickness in the structures. The unsteady Bernoulli equation and the circulation theorem are applied in order to express the aerodynamic pressure as the function of the vortex density. The vortex density is then obtained with the vortex lattice method considering the coupling boundary condition. From the analytical expressions of the unstable critical wind velocities, numerical results and some useful conclusions are obtained. It is found that the initial curvature of open cable-membrane structures has clear influence on the critical wind velocities of the structures.展开更多
Based on the assumption of gas-liquid stratified flow pattern in inclined gas wells,considering the influence of wettability and surface tension on the circumferential distribution of liquid film along the wellbore wa...Based on the assumption of gas-liquid stratified flow pattern in inclined gas wells,considering the influence of wettability and surface tension on the circumferential distribution of liquid film along the wellbore wall,the influence of the change of the gas-liquid interface configuration on the potential energy,kinetic energy and surface free energy of the two-phase system per unit length of the tube is investigated,and a new model for calculating the gas-liquid distribution at critical conditions is developed by using the principle of minimum energy.Considering the influence of the inclination angle,the calculation model of interfacial friction factor is established,and finally closed the governing equations.The interface shape is more vulnerable to wettability and surface tension at a low liquid holdup,resulting in a curved interface configuration.The interface is more curved when the smaller is the pipe diameter,or the smaller the liquid holdup,or the smaller the deviation angle,or the greater gas velocity,or the greater the gas density.The critical liquid-carrying velocity increases nonlinearly and then decreases with the increase of inclination angle.The inclination corresponding to the maximum critical liquid-carrying velocity increases with the increase of the diameter of the wellbore,and it is also affected by the fluid properties of the gas phase and liquid phase.The mean relative errors for critical liquid-carrying velocity and critical pressure gradient are 1.19%and 3.02%,respectively,and the misclassification rate is 2.38%in the field trial,implying the new model can provide a valid judgement on the liquid loading in inclined gas wells.展开更多
To clarify the existence of liquid loading and optimize the production allocation in gas wells,we constructed a model for calculating the critical liquid-carrying velocity based on the equal relationship between the t...To clarify the existence of liquid loading and optimize the production allocation in gas wells,we constructed a model for calculating the critical liquid-carrying velocity based on the equal relationship between the total surface free energy of droplets and the total turbulent kinetic energy of gas and considering the droplet size,droplet deformation and the influence of droplet deformation on surface free energy.Based on the ellipsoid hypothesis and by analyzing the influence of droplet deformation on the surface area and free energy of droplets,the equation for calculation of the maximum diameter of windward surface of droplets was developed.With consideration to the influence of droplet deformation on drags,the expression for the critical liquid-carrying velocity of ellipsoid droplets was clarified.With consideration to the influence of deformation and internal flow of droplets,the drag coefficient of the ellipsoid droplets was determined to be 20%higher than that of the Brauer Model for spheroid.A functional relationship between the deformation parameter K and the critical Weber number W_(ec) was established based on the energy conservation law.In addition,the calculation results were reduced by 10%.During the course,the impacts of gas-well pressure and temperature on surface tension were taken into account.The proposed model was compared with the models developed by Turner,Li Min,Wang Yizhong,Wang Zhibin and Xiong Yu,and on-site verification was conducted in 44 gas wells.The results show that the proposed model provides the prediction results in best coincidence with the actual performance of gas wells.In conclusion,the proposed model can be used to predict liquid loading in gas wells effectively.展开更多
Wet gas can form liquid loading at the lower line pipe sections,so the transportation efficiency will be impacted and the line pipes will be corroded and even blocked.Therefore,to accurately predict the critical liqui...Wet gas can form liquid loading at the lower line pipe sections,so the transportation efficiency will be impacted and the line pipes will be corroded and even blocked.Therefore,to accurately predict the critical liquid-carrying velocity of gas is of great significance to preventing the liquid loading in wet gas line pipes.In view of the gaseliquid two-phase stratified flow in micro-tilting line pipes with low liquid content,this paper newly established a critical liquid-carrying velocity prediction model considering droplet entrainment according to the momentum balance equation of a gaseliquid two-phase flow and the closure relationship of a new gaseliquid interface shape.Then,based on the experimental data,the new model,FLAT model,ARS model,double-circle model and MARS model were verified and their prediction results were compared.Finally,the new model was applied to analyze the effects of pipe dip,operational pressure,liquid density and gas component on the critical liquid-carrying velocity and critical liquid content of natural gasewater and natural gase-60%glycerine with water stratified flow in a microtilting line pipe.And the following research results were obtained.First,with the increase of pipe dip and liquid density,the critical liquidcarrying velocity increases continuously and the critical liquid content decreases gradually.Second,with the increase of operational pressure and heavy component content,the critical liquid-carrying velocity decreases continuously and the critical liquid content increases gradually.In conclusion,the new model is higher in prediction accuracy and its prediction result is better accordant with the experimental value,so it can be used to predict the critical liquid-carrying velocity in wet gas line pipes.展开更多
Aircraft laminated composite components often suffer a variety of high velocity impacts with large quantity of energy,which usually affects aircraft behavior and would incur component damages,even disastrous consequen...Aircraft laminated composite components often suffer a variety of high velocity impacts with large quantity of energy,which usually affects aircraft behavior and would incur component damages,even disastrous consequences.Therefore,one investigates the impact resistance of a new type of composite material,Ti/CFRP/Ti sandwich structure,and launches impact tests by using an air gun test system.Then one acquires the critical breakthrough rate of the structure and analyzes the damages.The results show that the main failure mode of the front titanium sheet is shear plugging and brittle fracture of adhesive layer with fiber breakage,while the back titanium sheet is severely ripped.The rear damage is worse than the front one.Compared with traditional CFRP laminates,the critical breakthrough rate of Ti/CFRP/Ti sandwich structure is improved by 69.9% when suffered the impact of a bearing ball with 2mm radius.展开更多
The propagation of shock waves in a cellular bar is systematically studied in the framework of continuum solids by adopting two idealized material models, viz. the dynamic rigid, perfectly plastic, locking （D-R-PP-L...The propagation of shock waves in a cellular bar is systematically studied in the framework of continuum solids by adopting two idealized material models, viz. the dynamic rigid, perfectly plastic, locking （D-R-PP-L） model and the dynamic rigid, linear hardening plastic, locking （D-R-LHP-L） model, both considering the effects of strain-rate on the material properties. The shock wave speed relevant to these two models is derived. Consider the case of a bar made of one of such material with initial length L 0 and initial velocity v i impinging onto a rigid target. The variations of the stress, strain, particle velocity, specific internal energy across the shock wave and the cease distance of shock wave are all determined analytically. In particular the ＂energy conservation condition＂ and the ＂kinematic existence condition＂ as proposed by Tan et al. （2005） is re-examined, showing that the ＂energy conservation condition＂ and the consequent ＂critical velocity＂, i.e. the shock can only be generated and sustained in R-PP-L bars when the impact velocity is above this critical velocity, is incorrect. Instead, with elastic deformation, strain-hardening and strain-rate sensitivity of the cellular materials being considered, it is appropriate to redefine a first and a second critical impact velocity for the existence and propagation of shock waves in cellular solids. Starting from the basic relations for shock wave propagating in D-R-LHP-L cellular materials, a new method for inversely determining the dynamic stress-strain curve for cellular materials is proposed. By using e.g. a combination of Taylor bar and Hopkinson pressure bar impact experimental technique, the dynamic stress-strain curve of aluminum foam could bedetermined. Finally, it is demonstrated that this new formulation of shock theory in this one-dimensional stress state can be generalized to shocks in a one-dimensional strain state, i.e. for the case of plate impact on cellular materials, by simply making proper replacements of the elastic and plastic constants.展开更多
文摘On the basis of analysing the outer performance degradation of shock absorber on suspenson and from the relationship between outer and inner performances of the shock absorber, an internal relationship between the structure design and degradation of the shock absorber is discussed in the paper. From dynamic property, analysed the dynamic cause for degradation, the paper proposes a technical method of improving outer performance and a concept of critical velocity, and discusses what effects the critical velocity and the outer performance mance degradation has.
基金supported by the Major State Basic Research Development Program of China(No.2011CB013101)the National Natural Science Foundation of China(No.10872003,10932001,11172001)+2 种基金the National Excellent Doctoral Dissertation of China(No.2007B2)the National Basic Research Program (973) of China(No.2008CB418203)the National Science and Technology Specific Project of China(No.20080ZX07422)
文摘Sediments are ultimate sinks of nutrients in lakes that record the pollution history evolutionary processes, and anthropogenic activities of a lake. However, sediments are considered as inner sources of environmental factor changes such as the variation in hydrodynamic conditions because of the nutrients they release. How does this process happen？ This study investigates a typical nutrient phosphorus （P） exchange among sediment, suspended particle matter （SPM）, and water. Compared with numerical and experimental studies, this study confirms that the critical velocity that occurs at a lower flow rate state exists in the range of 7 to 15 crn/sec. Critical velocity below the critical flow rate promotes the migration of particulate phosphorus （PP） to the SPM. On the other hand, critical velocity above the critical flow rate promotes the release of PP in water.
文摘The dynamics of the moving-with-constant-velocity internal pressure acting on the inner surface of the hollow circular cylinder surrounded by an infinite elastic medium is studied within the scope of the piecewise homogeneous body model by employing the exact field equations of the linear theory of elastodynamics.It is assumed that the internal pressure is point-located with respect to the cylinder axis and is axisymmetric in the circumferential direction.Moreover,it is assumed that shear-spring type imperfect contact conditions on the interface between the cylinder and surrounding elastic medium are satisfied.The focus is on the influence of the mentioned imperfectness on the critical velocity of the moving load and this is the main contribution and difference of the present paper the related other ones.The other difference of the present work from the related other ones is the study of the response of the interface stresses to the load moving velocity,distribution of these stresses with respect to the axial coordinates and to the time.At the same time,the present work contains detail analyses of the influence of problem parameters such as the ratio of modulus of elasticity,the ratio of the cylinder thickness to the cylinder radius,and the shear-spring type parameter which characterizes the degree of the contact imperfection on the values of the critical velocity and stress distribution.Corresponding numerical results are presented and discussed.In particular,it is established that the values of the critical velocity of the moving pressure decrease with the external radius of the cylinder under constant thickness of that.
基金Project supported by the YEQISUN Joint Funds of the National Natural Science Foundation of China(No.U2341231)the National Natural Science Foundation of China(No.12172186)。
文摘In most practical engineering applications,the translating belt wraps around two fixed wheels.The boundary conditions of the dynamic model are typically specified as simply supported or fixed boundaries.In this paper,non-homogeneous boundaries are introduced by the support wheels.Utilizing the translating belt as the mechanical prototype,the vibration characteristics of translating Timoshenko beam models with nonhomogeneous boundaries are investigated for the first time.The governing equations of Timoshenko beam are deduced by employing the generalized Hamilton's principle.The effects of parameters such as the radius of wheel and the length of belt on vibration characteristics including the equilibrium deformations,critical velocities,natural frequencies,and modes,are numerically calculated and analyzed.The numerical results indicate that the beam experiences deformation characterized by varying curvatures near the wheels.The radii of the wheels play a pivotal role in determining the change in trend of the relative difference between two beam models.Comparing the results unearths that the relative difference in equilibrium deformations between the two beam models is more pronounced with smaller-sized wheels.When the two wheels are of equal size,the critical velocities of both beam models reach their respective minima.In addition,the relative difference in natural frequencies between the two beam models exhibits nonlinear variation and can easily exceed 50%.Furthermore,as the axial velocities increase,the impact of non-homogeneous boundaries on modal shape of translating beam becomes more significant.Although dealing with non-homogeneous boundaries is challenging,beam models with non-homogeneous boundaries are more sensitive to parameters,and the differences between the two types of beams undergo some interesting variations under the influence of non-homogeneous boundaries.
基金supported by the National Basic Research Program of China (973 Program)(No. 2006CB601202)the Open Foundation of State Key Laboratory of Structural Analysis of Indus-trial Equipment of China (No. GZ0701)the Doctoral Foundation of Northwestern PolytechnicalUniversity (No. CX200810)
文摘Critical velocity of an infinite long sandwich shell under moving internal pressure is studied using the sandwich shell theory and elastodynamics theory. Propagation of axisymmetric free harmonic waves in the sandwich shell is studied using the sandwich shell theory by considering compressibility and transverse shear deformation of the core, and transverse shear deformation of face sheets. Based on the elastodynamics theory, displacement components expanded by Legendre polynomials, and position-dependent elastic constants and densities are introduced into the equations of motion. Critical velocity is the minimum phase velocity on the desperation relation curve obtained by using the two methods. Numerical examples and the finite element （FE） simulations are presented. The results show that the two critical velocities agree well with each other, and two desperation relation curves agree well with each other when the wave number k is relatively small. However, two limit phase velocities approach to the shear wave velocities of the face sheet and the core respectively when k limits to infinite. The two methods are efficient in the investigation of wave propagation in a sandwich cylindrical shell when k is relatively small. The critical velocity predicted in the FE simulations agrees with theoretical prediction.
基金supported by the National Natural Science Foundation of China(Nos.52405356,52061135101,52071265)Jiangxi Provincial Natural Science Foundation Project,China(No.20242BAB20200)the National Key Research and Development Program,China(No.2021YFB3200500).
文摘The particle acceleration behavior and deposition mechanism of cold spraying aluminum matrix composites(Al_(2)O_(3)/2024)are complicated by the addition of ceramic particles.The effects of different feeding rates and particle diameters on critical velocity and mechanical properties were studied by numerical simulation and experiment.The results indicate that as the powder feeding rate increases,the impact velocity of gas and particles gradually decreases,and the temperature of gas and particles increases,resulting in an increase in the difference between particle impact velocity and critical velocity.The highest tensile strength of the deposit is achieved at a powder feeding rate of 1 r/min,which is 343 MPa.As the powder feeding rate increases,the performance of the deposits decreases,but it significantly saves time and cost.As the particle diameter increases,the impact temperature first increases and then decreases,resulting in the critical velocity first decreasing and then increasing,and the mechanical performance first increasing and then decreasing.To some extent,the best performance of the deposit is achieved when the size of the metal particle is close to that of the ceramic particle.
文摘Presents the calculation of critical velocity, natural frequency and dynamic respondency of fluid conveying pipe are calculated under different boundary conditions using finite element method, and the use of calculation results to design and research rocket pipes feeding fuel and watery turbine pipes conveying water etc.
基金the National Natural Science Founda-tion of China(No.51675324)the Shanghai Founda-tion for University Key Teacher(No,ZZGCD15039)New Energy Vehicle Vibration and Noise Test and Control Professional Technical Service Platform(No.18DZ2295900)。
文摘In actual line operation,the critical velocity is one of the key physical quantities of rail design owing to its great infuence on the riding comfort and safety of vehicles due to the wheel-rail contact loss caused by the abrupt change of rail foundation rigidity,rail wear,or abruptness irregularities on rail.In this study,the short floating slab track(SFST)structure is regarded as a double-layer system.The Euler beam and the rigid body model are adopted for the rail and the floating slab,respectively.and the dispersion equation and the theoretical critical velocity of the rail structure under ideal conditions are deduced.Besides,this st udy considers the implementation of the SFST in the vehicle-structure coupling system.The alterable element method is introduced for accurately simulating the change of the whee-rail contact state and coding a vehicle-structure dynamic analysis program(VSDAP)to calculate the critical velocity of rail structures from the dynamic response of vehicles and rail structures.The principle of its design at the beginning of the design is given on the basis of the theoretical value of the critical velocity and the simulation of the dynamic response,which can provide reference for practical engineering design.
基金This work was supported by the Science Research and Technology Development Foundation Project of China National Petroleum Corporation(grant No.2023DQ03-11)。
文摘Accurately predicting the minimum velocity required to initiate particles movement on a cuttings bed surface during drilling operations is crucial for efficient and cost-effective removal of deposited particles.However,current models neglect the influence of particle shape on the drag coefficient and static friction coefficient during rolling and sliding on a cuttings bed.Accordingly,this study developed an experimental setup for cuttings transport and employed both theoretical analysis and experimental methods to investigate the critical velocity for the incipient motion of particles under various operational conditions.A novel semi-mechanical criterion model was developed for the incipient motion of particles,incorporating a shape correction factor for non-spherical particles.A balance equation for the threshold Shields number,determined by particle driving forces and resistances,was established,and a numerical procedure was formulated to determine the critical velocity for the incipient motion of particles.The model predictions show strong agreement with experimental results.The study found that higher eccentricity,inclination,and fluid viscosity increased the difficulty of initiating particle movement on the cuttings bed surface,thus requiring higher annular velocities for effective cuttings removal.Conversely,increasing particle size facilitated easier removal of the cuttings bed.Compared to non-Newtonian fluids,Newtonian fluids proved more effective in cuttings removal.The findings of this study are significant for optimizing hole cleaning parameters and improving the efficiency of cuttings removal.
基金This research was supported by the National Nature Science Foundation of China(No.52076066)Key Research and Development Project of Zhejiang Province(No.2018C03029)+1 种基金Zhejiang Provincial Natural Science Foundation of China(No.LQ19E040005)Fellowship of China Postdoctoral Science Foundation(No.2021M693042).
文摘The objective of this study is to investigate critical velocity and smoke maximum temperature beneath the ceiling in the connected area of branch tunnel with varying fire locations.The fire sources were located in the divergent connected area of the branch tunnel,to imitate traffic accidents near the branch point.A 1/20 scale model branch tunnel was built including main line before branch,main line after branch,and ramp.Experimental tests and numerical simulations were performed to explore smoke movement characteristics with longitudinal ventilation.The results showed that the enlarged cross-sectional area in branch tunnel caused the shortening of the back-layering length,and a modified model of back-layering length was proposed.The higher tunnel height in this work affected the critical condition of large fire;it caused a larger transition point of dimensionless critical velocity.A revised model was proposed for the maximum temperature rise of tunnel fires in the connected area of branch tunnel.The critical velocity kept unchanged when the branch angle increased from 0°to 20°because there is little change in the longitudinal smoke temperature.As the local tunnel width of fire source was increased,the required critical velocity was increased while the local effective velocity kept nearly the same.
基金The authors of this paper would like to thank the financial supports provided by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant XDA22000000).
文摘Hydraulic collecting and pipe transportation are regarded as an efficient way for exploiting submarine mineral resources such as the manganese nodules and ores.Coarse particles on the surface of the sea bed are sucked by a pipe during the mining and crushing of the mineral.In this paper,the critical suction velocity for lifting the coarse particles is investigated through a series of laboratory experiments,and the solid-liquid two-phase flow characteristics are obtained.Based on the dimensional analysis,the geometric similarity is found between actual exploitation process and model test with the same kind of material.The controlling dimensionless parameters such as the hydraulic collecting number,the relative coarse particle diameter,the relative suction height,and the density ratio are deduced and discussed.The results show that the logarithm in base 10 of the hydraulic collecting number increases approximately linearly with the increase of the relative suction height,while decreases with the relative particle diameter.A fitting formula for predicting the critical suction velocity is presented according to the experimental results.
基金supporting by the Youth Program of National Natural Science Foundation of China(52104012)the China Postdoctoral Science Foundation(2021M693494)+2 种基金the Key Program of the National Natural Science Foundation of China(51734010)the Key Natural Science Projects of Scientific Research Plan in Colleges and Universities of Xinjiang Uygur Autonomous Region(XJEDU2021I028)the Strategic Cooperation Technology Projects of CNPC and CUPB(ZLZX2020-01-01)
文摘The purpose of this paper is to study the critical sand starting velocity and transformation law of flow pattern based on gas-water-sand three-phase flow in an inclined pipe.Firstly,the indoor simulation experiment system of gas-water-sand three-phase flow was used to test the conversion law of flow pattern based upon the different gas void fraction.Secondly,the influence of slug bubbles on sand migration was investigated according to distinctive hole deviation angles,gas void fraction and sand concentration.Finally,the critical sand starting velocity was tested based on dissimilar hole deviation angles,gas void fraction,sand concentration and sand particle size,and then the influence of the abovementioned key parameters on the sand starting velocity was debated based on the force analysis of the sand particles.The experimental results illustrated that when the gas void fraction was less than 5%,it was bubbly flow.When it increased from 5%to 30%,the bubbly flow and slug flow coexisted.When it was between 30%and 50%,the slug flow and agitated flow coexisted.When it reached 50%,it was agitated flow.Providing that the hole deviation angle was 90°,the phenomenon of overall migration and wavelike migration on the surface of sand bed was observed.On the contrary,the phenomenon of rolling and jumping migration was recognized.The critical sand starting velocity was positively correlated with the hole deviation angle and sand particle size,but negatively associated with the gas void fraction and sand concentration.This research can provide a certain reference for sand-starting production in the field of petroleum engineering.
基金Supported by the Shanghai Municipal Infor mation Fund Project (2004)
文摘Full-scale numerical experiments were carried out on the vehicular fire in a long tunnel to study the critical ventilation velocity and back-layer distance with heat release rate of 5, 20 and 100 MW respectively. A computational fluid dynamics (CFD) model of fire-driven fluid flow FDS(Fire Dynamics Simulator) was used to solve numerically a form of the Navier-Stokes equations for fire. The results were compared with the expressions proposed in the literature. A modified equation for the critical ventilation velocity was given to better fit the experimental results. A bi-exponential model that well fitted the numerical experimental results was proposed to describe the relationship between back-layer distance and ventilation velocity.
基金Supported by National Natural Science Foundation of China(Grant Nos.51275557,51422505)
文摘The current research of direct yaw moment control（DYC） system focus on the design of target yaw moment and the distribution of wheel brake force. The differential braking intervention can effectively improve the lateral stability of the vehicle, however, the effect of DYC can be improved a step further by applying the control of vehicle longitudinal velocity. In this paper, the relationship between the vehicle longitudinal velocity and lateral stability is studied, and the simulation results show that a decrease of 5 km/h of longitudinal velocity at a particular situation can bring 100° increasing of stable steering upper limit. A critical stable velocity considering the effect of steering and yaw rate measurement is defined to evaluate the risk of losing steer-ability or stability. A novel velocity pre-control method is proposed by using a hierarchical pre-control logic and is integrated with the traditional DYC system. The control algorithm is verified through a hardware in-the-loop simulation system. Double lane change（DLC） test results on both high friction coefficient（μ） and low μ roads show that by using the pre-control method, the steering effort in DLC test can be reduced by 38% and 51% and the peak value of brake pressure control can be reduced by 20% and 12% respectively on high μ and low μ roads, the lateral stability is also improved. This research proposes a novel DYC system with lighter control effort and better control effect.
基金supported by the Natural Science Foundation of Guangdong Province of China (No. 020904)
文摘The aerodynamic unstable critical wind velocity for three-dimensional open cable-membrane structures is investigated. The geometric nonlinearity is introduced into the dynamic equilibrium equations of structures. The disturbances on the structural surface caused by the air flow are simulated by a vortex layer with infinite thickness in the structures. The unsteady Bernoulli equation and the circulation theorem are applied in order to express the aerodynamic pressure as the function of the vortex density. The vortex density is then obtained with the vortex lattice method considering the coupling boundary condition. From the analytical expressions of the unstable critical wind velocities, numerical results and some useful conclusions are obtained. It is found that the initial curvature of open cable-membrane structures has clear influence on the critical wind velocities of the structures.
基金Supported by National Natural Science Foundation of China(21978171)。
文摘Based on the assumption of gas-liquid stratified flow pattern in inclined gas wells,considering the influence of wettability and surface tension on the circumferential distribution of liquid film along the wellbore wall,the influence of the change of the gas-liquid interface configuration on the potential energy,kinetic energy and surface free energy of the two-phase system per unit length of the tube is investigated,and a new model for calculating the gas-liquid distribution at critical conditions is developed by using the principle of minimum energy.Considering the influence of the inclination angle,the calculation model of interfacial friction factor is established,and finally closed the governing equations.The interface shape is more vulnerable to wettability and surface tension at a low liquid holdup,resulting in a curved interface configuration.The interface is more curved when the smaller is the pipe diameter,or the smaller the liquid holdup,or the smaller the deviation angle,or the greater gas velocity,or the greater the gas density.The critical liquid-carrying velocity increases nonlinearly and then decreases with the increase of inclination angle.The inclination corresponding to the maximum critical liquid-carrying velocity increases with the increase of the diameter of the wellbore,and it is also affected by the fluid properties of the gas phase and liquid phase.The mean relative errors for critical liquid-carrying velocity and critical pressure gradient are 1.19%and 3.02%,respectively,and the misclassification rate is 2.38%in the field trial,implying the new model can provide a valid judgement on the liquid loading in inclined gas wells.
基金Project supported by the Postdoctoral Research Project of Shaanxi Province“Study on the gas/liquid two-phase helical vortex flow characteristics in the vortex shaft caused by spiral guide plate”(No.2016BSHEDZZ25).
文摘To clarify the existence of liquid loading and optimize the production allocation in gas wells,we constructed a model for calculating the critical liquid-carrying velocity based on the equal relationship between the total surface free energy of droplets and the total turbulent kinetic energy of gas and considering the droplet size,droplet deformation and the influence of droplet deformation on surface free energy.Based on the ellipsoid hypothesis and by analyzing the influence of droplet deformation on the surface area and free energy of droplets,the equation for calculation of the maximum diameter of windward surface of droplets was developed.With consideration to the influence of droplet deformation on drags,the expression for the critical liquid-carrying velocity of ellipsoid droplets was clarified.With consideration to the influence of deformation and internal flow of droplets,the drag coefficient of the ellipsoid droplets was determined to be 20%higher than that of the Brauer Model for spheroid.A functional relationship between the deformation parameter K and the critical Weber number W_(ec) was established based on the energy conservation law.In addition,the calculation results were reduced by 10%.During the course,the impacts of gas-well pressure and temperature on surface tension were taken into account.The proposed model was compared with the models developed by Turner,Li Min,Wang Yizhong,Wang Zhibin and Xiong Yu,and on-site verification was conducted in 44 gas wells.The results show that the proposed model provides the prediction results in best coincidence with the actual performance of gas wells.In conclusion,the proposed model can be used to predict liquid loading in gas wells effectively.
基金supported by National Natural Science Foundation of China“Thermodynamic behavior investigation,energy efficiency analysis and structural optimization of longitudinal finned tubes of air-heated vaporizer in the integrated cold energy thermoelectric generator”and“Enhanced heat transfer mechanism and structural optimization of innovative heat transfer tube of open rack vaporizer”(No.:51774237 and 51304160)Shaanxi Provincial Scientific Project for Postdoctors“Study on kinetic behaviors of gaseliquid two-phase swirling flow caused by helical tape in vortex borehole”(No.:20168630)Special Research Program of the Education Department of Shaanxi Province“Integration and optimization of cold energy utilization and light hydrocarbon recycling processes at LNG receiving terminal based on the multi-objective comprehensive evaluation method”(No.:15JK1581).
文摘Wet gas can form liquid loading at the lower line pipe sections,so the transportation efficiency will be impacted and the line pipes will be corroded and even blocked.Therefore,to accurately predict the critical liquid-carrying velocity of gas is of great significance to preventing the liquid loading in wet gas line pipes.In view of the gaseliquid two-phase stratified flow in micro-tilting line pipes with low liquid content,this paper newly established a critical liquid-carrying velocity prediction model considering droplet entrainment according to the momentum balance equation of a gaseliquid two-phase flow and the closure relationship of a new gaseliquid interface shape.Then,based on the experimental data,the new model,FLAT model,ARS model,double-circle model and MARS model were verified and their prediction results were compared.Finally,the new model was applied to analyze the effects of pipe dip,operational pressure,liquid density and gas component on the critical liquid-carrying velocity and critical liquid content of natural gasewater and natural gase-60%glycerine with water stratified flow in a microtilting line pipe.And the following research results were obtained.First,with the increase of pipe dip and liquid density,the critical liquidcarrying velocity increases continuously and the critical liquid content decreases gradually.Second,with the increase of operational pressure and heavy component content,the critical liquid-carrying velocity decreases continuously and the critical liquid content increases gradually.In conclusion,the new model is higher in prediction accuracy and its prediction result is better accordant with the experimental value,so it can be used to predict the critical liquid-carrying velocity in wet gas line pipes.
基金funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘Aircraft laminated composite components often suffer a variety of high velocity impacts with large quantity of energy,which usually affects aircraft behavior and would incur component damages,even disastrous consequences.Therefore,one investigates the impact resistance of a new type of composite material,Ti/CFRP/Ti sandwich structure,and launches impact tests by using an air gun test system.Then one acquires the critical breakthrough rate of the structure and analyzes the damages.The results show that the main failure mode of the front titanium sheet is shear plugging and brittle fracture of adhesive layer with fiber breakage,while the back titanium sheet is severely ripped.The rear damage is worse than the front one.Compared with traditional CFRP laminates,the critical breakthrough rate of Ti/CFRP/Ti sandwich structure is improved by 69.9% when suffered the impact of a bearing ball with 2mm radius.
基金supported by the National Natural Science Foundation of China (11032001)the K.C.Wong Magna Fund in Ningbo University
文摘The propagation of shock waves in a cellular bar is systematically studied in the framework of continuum solids by adopting two idealized material models, viz. the dynamic rigid, perfectly plastic, locking （D-R-PP-L） model and the dynamic rigid, linear hardening plastic, locking （D-R-LHP-L） model, both considering the effects of strain-rate on the material properties. The shock wave speed relevant to these two models is derived. Consider the case of a bar made of one of such material with initial length L 0 and initial velocity v i impinging onto a rigid target. The variations of the stress, strain, particle velocity, specific internal energy across the shock wave and the cease distance of shock wave are all determined analytically. In particular the ＂energy conservation condition＂ and the ＂kinematic existence condition＂ as proposed by Tan et al. （2005） is re-examined, showing that the ＂energy conservation condition＂ and the consequent ＂critical velocity＂, i.e. the shock can only be generated and sustained in R-PP-L bars when the impact velocity is above this critical velocity, is incorrect. Instead, with elastic deformation, strain-hardening and strain-rate sensitivity of the cellular materials being considered, it is appropriate to redefine a first and a second critical impact velocity for the existence and propagation of shock waves in cellular solids. Starting from the basic relations for shock wave propagating in D-R-LHP-L cellular materials, a new method for inversely determining the dynamic stress-strain curve for cellular materials is proposed. By using e.g. a combination of Taylor bar and Hopkinson pressure bar impact experimental technique, the dynamic stress-strain curve of aluminum foam could bedetermined. Finally, it is demonstrated that this new formulation of shock theory in this one-dimensional stress state can be generalized to shocks in a one-dimensional strain state, i.e. for the case of plate impact on cellular materials, by simply making proper replacements of the elastic and plastic constants.
